I suspect a water jet is not as efficient as a propellor.
Since you are evidently planning on 12v on your cat, why don't you get a
small 12v trolling motor ? That would take dumkings better than a gas motor,
although you would need to rinse it off.

"Shaun Van Poecke" wrote in message
...
ok, Ive heard this idea brought up before and seen it poo poo'd, but can
it work to some extent?

Ive got a 14' cat that i store next to the beach in sydney harbour and i
like to get out for a sail when i can. Unlike most cats this size, it has
heaps of flotation - 3-4 adults and still not sinking anywhere near as
much as a hobie 14 with 2 POB. It has an outboard bracket on the back
which was on it from the factory, but i've destroyed 2 admittedly cheap
and nasty second hand outboards on it so far. I have a new honda 2hp 4
stroke on my dinghy that i dont want to put on the cat because it would
probably suffer a similar fate.

What happens is that because your moving so fast, the outboard gets
completely drowned, as do the people sailing for that matter ;-) an
outboard might work on a lake or something, but sydney harbour gets
choppy. The thing is, this boat was designed for island hopping the
whitsundays and the manufacturer claims enough flotation for 4 people,
plus camping gear, a stove, and food and water for a week! I cant see how
they get the outboard to survive...

i do ok if i get the outboard started and there are no waves and i just
motor round on it. a 2 or 3 is plenty to move along. its rated for a 5
at maximum. the trouble is, as soon as you sail if there's a bit of chop,
that motor is getting a drink - then you'll never get it started. I want
a bit of propulsion for getting into some of the finnicky bay areas rather
than spending a couple of hours tacking to death, 5 minutes of propulsion
would get me there. propulsion would also be nice for getting back in if
the wind dies, and finally as a backup just in case something breaks. i
like to go out when the wind is big, and ive already had a couple of
incidents with snapping a gooseneck fitting, and destoying a couple of jib
cleats.

so here's what im thinking; a 1250GPH bilge pump in each hull, intake
hoses going into the water, outlets hooked up to hoses facing rear. these
draw 5A each and are cheap to buy. A 40-50AH sealed gel cell would give
me a lot more power than i need. I cant see myself using ot for longer
than about 30 minutes to an hour at a time. Is this going to move me at
all? at least more than trying to paddle the boat by myself (which gets
me almost nowhere!) would i get any benefit from using smaller diameter
hoses to create a stronget 'jet', or am i just unnecessarily loading the
pump for no real gain? am i miles off in the GPH stakes.... do i need a
lot more pumping to get any effect?

im not looking for a speed boat here, just *movement* even 1 knot would
be something. benefits to this system are that its fully submersible,
completely unobtrusive, almost silent, would cost me about $100, starts
instantly when i need it.

thanks,
Shaun